Record pdf load result and time in Android

onLoadDocumentSuccess / onLoadDocumentError callback may be invoked
on PdfViewerFragment restoration.
We do not #setDocumentUri and record Android.Pdf.DocumentLoad for
these cases.
To have comparable records counts, DocumentLoadResult and
DocumentLoadTime should only be recorded when there is a paired
Android.Pdf.DocumentLoad.

Low-Coverage-Reason: TRIVIAL_CHANGE
Bug: 375041802
Change-Id: I7c2f6066badb2d992a32ba1d126106c5af8e8e39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5954033


Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Reviewed-by: Sirisha Kavuluru <skavuluru@google.com>
Commit-Queue: Shu Yang <shuyng@google.com>
Cr-Commit-Position: refs/heads/main@{#1372451}